Heretofore, there have been developed AV devices which are capable of transmitting information with each other through a network using an IEEE 1394 serial data bus prescribed by the IEEE (The Institute of Electrical and Electronics Engineers), for example. In this network, a user is able to control the AV devices connected to the above network with each other by using a predetermined command (AV/C Command Transaction Set: hereinafter abbreviated as an “AV/C command”). The details of the IEEE 1394 system and the details of the AV/C command are described in the AV/C Digital Interface Command Set General Specification which is laid open in the 1394 Trade Association.
As shown in FIG. 1, when an IEEE 1394 serial data bus 51 (hereinafter referred to as a “bus 51”) is used, video data received by an IRD (Integrated Receiver Decoder) 52, which is a digital satellite receiver for receiving and decoding a digital satellite broadcasting, for example, can be recorded by a DVCR (Digital Video Cassette Recorder) 53 connected to the integrated receiver decoder via the bus 51. Further, video data can be recorded by these IRD 52 and DVCR 53 in a so-called timer-activated recording fashion under control of the AV/C command.
When video data is recorded by this apparatus in a timer-activated recording mode the IRD 52 and the DVCR 53 are controlled by a controller 54 provided within the IRD 52, for example. In this case, the setting (channel, start time, etc.) of the timer-activated recording is effected on the IRD 52. At the set start time, the controller 54 outputs a command to a digital tuner 55 provided within the IRD 52 so that the digital tuner may select the set channel and that a video signal or the like received by the digital tuner 85 from signals received at an antenna 56 is output to the bus 81.
At the same time, a recording start command is transmitted from the controller 54 through the bus 51 to a recorder 57 provided within the DVCR 53. Consequently, the recorder 57 obtains the video signal or the like selected and received at the digital tuner 55 from the bus 51 and records the same on a recording medium such as a magnetic tape. The timer-activated recording is made in this manner. Further, the DVCR 53 also includes a controller 58 to effect a control such as recording a video signal or the like received at an analog tuner 59 incorporated therein by the recorder 57.
When the AV/C command, which controls the devices connected to the network by the remote controller, shares information within the devices with other devices as described above, it has been customary that information is shared by setting lists to the control target subunit such as a VCR subunit and a tuner subunit. However, according to the above method, the contents of the shared information are limited to those relating to the respective subunits. In accordance with the development of the future network system, there is a possibility that the contents of shared information will not be limited to those unique to the subunits but a demand of handling information of various contents will increase.
On the other hand, the assignee of the present application has previously proposed an AV/C Bulletin Board Subunit (AV/C Bulletin Board Subunit hereinafter abbreviated as a “BBS”) as a space for sharing information independent of subunits (see the 1394 Trade Association Board Subunit General Specification, Rev. 0.38). According to this system, the BBS can share arbitrary information thereby to control arbitrary devices with each other.
However, in the previously-proposed BBS, a method required when boards of a plurality of types should coexist and a list structure required when a plurality of boards of the same type should exist are not definite, and hence a variety of data cannot be stored efficiently. Accordingly when data is read out from another device or data is written in another device, data should be processed after all data had been read out from the BBS, for example, with the result that processing becomes complicated. Therefore there is an increasing demand of efficiently writing and reading data by using the BBS.